Answer Acceptable answers Mark. Answer Acceptable answers Mark. Answer Acceptable answers Mark. accept: 3 : 1. Answer Acceptable answers Mark

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1 1a(i) answers must be in this order. dominant HH 1a(ii) 1a(iii) H h H HH Hh h Hh hh 1 mark for correct gametes 1 mark for correct offspring If incorrect gametes allow 1 mark for correct Punnett square based on selected gametes accept error carried forward from their Punnett square 75% / ¾ / 0.75 accept: 3 : 1 1b(i) An explanation linking two of the following: Huntington s disease is caused by a dominant allele / CF is caused by a recessive allele only one allele for Huntington s disease needs to be inherited to have the disease / would have the disease if heterozygous (or homozygous dominant) two alleles (recessive) need to be inherited to have CF / be homozygous recessive for CF Ignore refs to gene for allele against this marking point Ignore refs to gene for allele against this marking point

2 b(ii) A mucus b(iii) An explanation linking two of the following: (thick / sticky / more) mucus builds up in the tubes (of the reproductive system) Reject: mucus in lungs/intestine accept sperm duct / vas deferens (the mucus) blocks the flow of sperm Total for question = 10 marks

3 2(a)(i) 2(a)(ii) XX ignore any superscript or subscript letters/symbols reject XY An explanation linking two of the following ignore gene throughout they did not inherit the (haemophilia) allele accept have the dominant/normal allele (allele is) located on X chromosome accept disorder is located on the X chromosome males receive X chromosome from their mother/y chromosome from father B is homozygous dominant/ neither X chromosome from B has the allele for haemophilia ignore mother is unaffected accept mother neither affected nor a carrier accept mother for B and father for A

4 2(a)(iii) H X Y X H X H X H X H Y X h X H X h X h Y a Punnett square showing the gametes of individuals C and D reject if allele shown on Y chromosome a Punnett square showing the genotypes of the offspring 25% / 0.25 / 1 in 4 probability of a child having haemophilia 50% of males have haemophilia Punnett square must be interpreted correctly (3)

5 2(b) An explanation linking the following aseptic conditions ignore sterile prevent growth of unwanted organisms/prevent contamination OR temperature /ph provide optimal conditions for growth /prevent enzymes denaturing provide optimal conditions for enzymes/prevent microorganisms being killed OR nutrient levels provide optimal conditions for growth OR aeration/oxygen for aerobic respiration/ provide optimal conditions for growth / prevent anaerobic respiration (Total for question 2 = 8 marks)

6 3a(i) homozygous recessive Accept in any order: homozygous recessive (alleles) 3(a)(ii) female gametes e e male gametes E Ee Ee e ee ee correct gametes in male/female gametes headings correct offspring genotypes 3a(iii) Any one of the following 1/2 Accept if 2 correct answers are given e.g. ½, 50% 0.50 evens chance 2/4 50 % 1:1 / 2:2

7 3(a)(iv) A 0% 3(b) A description including the following points reference to mucus Accept three symptoms described (3) Ignore: references to symptoms of sickle cell location described e.g. lungs / pancreas / reproductive system consequence described e.g. breathing difficulty / infection / weight loss due to blocking of enzymes / difficulty with digestion or absorption / infertility Accept airways for lungs Accept fertility problems for infertility Symptoms may include diabetes malnutrition incontinence in females sinusitis nasal polyps arthritis (3)

8 4(a)(i) D 4(a)(ii) substitution e.c.f from 3(a)(i) evaluation x (%) accept 68(%) for 2 marks give full marks for correct answer, no working 4(b)(i) Female gametes b b B Bb Bb Male gametes b bb bb gametes in male/female gametes headings offspring genotypes 4(b)(ii) 0.5 / 50% / 50/50 / ½ / 2/4 / evens 2:2 /even chance

9 4(b)(iii) homozygous recessive Accept any reasonable spelling of the term Reject heterozygous homozygous recessive 4 (c) an explanation linking three of the following speciation different geographical area may have different selection pressures / environmental conditions those individuals of a species suited /adapted / to this environment will survive and breed named environmental conditions e.g. clima Accept survival of the fittest adaptations/genes passed down to the offspring new species unable to breed with original (3)

10 5(a)(i) 2 / two (offspring) 2 and 3 5(a)(ii) D 5(a)(iii) An explanation linking two of the following points: two of the offspring from generation II had CF the children with cystic fibrosis must have inherited 1 recessive allele from each parent / children must have 2 recessive alleles both parents must have 1 recessive allele / be carriers of the CF allele ORA if homozygous dominant then no CF offspring Ignore: references to genes ORA if homozygous recessive offspring would have CF

11 5(b) correct gametes correct offspring B b Accept bb instead of Bb B BB Bb b Bb bb 5(c) An explanation linking two of the following: pedigree analysis will determine the likelihood that their offspring could inherit the CF allele if heterozygous there is a 50% chance (that the CF allele) will be passed on / if 2 heterozygous parents 25% chance the offspring will have CF Accept to see if they are a carrier of the CF allele Accept ratios rather than percentages 2 in 4 chance if either parent is homozygous dominant there is 0% chance that their offspring could have the disease